The present invention relates generally to rotary hand tools, and, more specifically, to a high speed pneumatic cut-off tool which is reversible, so as to be capable of selective rotation of the cutting wheel in either the clockwise or counter-clockwise direction.
Conventional rotary power cut-off tools have been provided only with the capability of rotating the cutting wheel in one direction. While rotary cut-off tools have many various applications, including numerous uses in and around the home, the present invention is particularly directed toward industrial uses with confined spaces and delicate, damageable surroundings or where especially high speeds of rotation and long periods of use may be required.
One of the drawbacks of rotary cut-off tools is that they tend to throw debris from the cut off the wheel as the material is cut. The debris is kicked off the wheel at a high velocity, and thus with a significant amount of force. Accordingly, anything which is impacted by the flying debris (which may include paint chips, sparks and metal slivers) may be scratched, gouged or otherwise marred. Likewise, a person positioned within the path of the flying debris may be injured, either by being struck by sparks or pieces of paint or metal moving at a high velocity, or by inhaling from the stream or cloud of dust produced by the cutting action.
Thus it is desirable to be able to control the direction in which the grinding wheel rotates, and thereby control the direction in which the resulting debris is thrown from the wheel, relative to the position of the object being cut and to the position of the user. Frequently in attempting to so control the flow of dust and debris, or similarly to control the direction of the wheel rotation for a specific effect on the workpiece, the power cut-off tool user is forced to assume a position which is at the least uncomfortable and perhaps even dangerous. Working for extended periods of time with the body twisted into an awkward position can result in long term physical problems, as well as increased fatigue and possible mistakes and accidents in the short run.
Although reversible motors are known for use in other hand-held power tools, such as commercially available drills and screwdrivers, they have not heretofore been successfully incorporated into high-speed rotary power cut-off tools. Rather, any attempt at using such a known motor in a reversible rotary power cut-off tool would have been unsatisfactory because in the reverse mode of operation the hub of the tool would become loose, and could literally fly across the room, with obvious dangerous consequences.
Thus it is an object of the present invention to provide a clamping hub for a reversible tool which can operate in a safe manner in both the clockwise and counter-clockwise directions, without risk of portions of the tool becoming loose and possibly airborne during use.
The present invention as described herein is described as it would be utilized in a reversible pneumatic cut-off tool. The use of the present invention is, however, not limited to pneumatically powered tools, nor is it limited to cut-off tools. Such a reversible clamping hub can be utilized in many applications including any rotary power tool which may operate in both the clockwise and counter-clockwise directions for which the workforce is axially clamped.
Briefly described, the present invention depends on the motor shaft of the cut-off tool which has been externally threaded with a left-hand thread. The shaft also has a hole drilled in its end and is internally threaded with a right hand thread. The tool head has a hex adapter which is internally threaded at its proximal end to accommodate the left-hand thread of the motor shaft. The hex adapter has a d-shaped hole bored into its distal end to accommodate the wheel retainer which has a corresponding external shape. The wheel retainer is hollow as to accommodate a right-hand threaded screw to be inserted through it and threaded into the corresponding internal threads of the motor shaft.
The two opposing threads in the tool head will keep it from coming loose and allowing the grinding wheel to become detached. When the tool is in clockwise operation or "forward" operation the right-hand screw will tighten causing the wheel retainer to lock the grinding wheel into place. When the tool is in counter-clockwise or "reverse" operation, the left-hand threaded hex adapter will tighten against the wheel retainer locking the wheel into place. Additionally, a non-rotational feature such as a d-slot and corresponding shape of the wheel retainer will prevent the rotation of the wheel retainer with respect to the hex adapter which might otherwise cause the screw to loosen. This novel feature is key to keeping the wheel retainer from accidentally disengaging.
The present invention is described more fully in the following drawings and description: